pistol in 9mm or bigger
decent holster
three magazines
four boxes (200 rounds of ammo)
ear protection (preferably both plugs and muffs to wear over them)
eye protection

Go to the first USPSA or IDPA match you can find.

Tell the match director or Chief Range Officer that this is your first match.

They will square you away. Then go slow, take your time, do not concern yourself with your score. Just BE SAFE amd shoot the best you can. It is my opinion that matches are the very best practice anyway!

Everyone in this sport wants it to grow safely, many will offer advice. Take what works, and that which does not was offered in good faith!